Speaker
Description
The rainbow effect is a fundamental phenomenon in any scattering theory of waves and particles, describing the accumulation of trajectories at characteristic angles due to extrema of the deflection function. In particular, the atomic rainbow effect – arising in semiclassical particle scattering due to singularities in the classical differential cross section – provides valuable information about the interaction potential between a projectile and target atoms, which is of particular interest for two-dimensional systems. However, experimental observation of the atomic rainbow effect in two-dimensional materials is highly challenging, as both an atomically clean target and a high-resolution detector are required.
Here, we present the experimental observation of rainbow scattering in ion transmission through single-layer graphene using time-of-flight medium energy ion scattering [1]. For 40 keV Xe$^{+}$ ions, the observed scattering pattern exhibits two distinct components: a circular outer rainbow at 5.28°, associated with maximum binary collision deflection from individual carbon atoms, and a hexagonal inner rainbow at 0.43°, originating from projectiles with characteristic trajectories interacting with multiple carbon atoms. Molecular dynamics and binary collision simulations reproduce these regimes and clarify their physical origins, but fail to capture the measured intensity distribution at the smallest deflection angles when using averaged radially symmetric interaction potentials. These results establish graphene rainbow scattering as an experimental benchmark for ion-solid interaction potentials and reveal limitations of commonly used approximations in describing many-body scattering dynamics. The cleanliness of the graphene sample is quantified using a recently developed method based on recoil-projectile coincidence in ion scattering experiments.
References
[1] C. Frank et al., Carbon 257 (2026)